Set arguments explicitly in CLI entrypoints

Set arguments explicitly in CLI entrypoints instead of letting
`argparse` handle it.

This allows us to determine whether any arguments were actually
provided without having to resort to checking `sys.argv`. This is done
more for the sake of tests, which relied on monkeypatching `sys.argv`
which is *very* flaky and broke tests in the Nix build sandbox and
potentially other environments as well.

Fixes #346

src/protontricks/cli/desktop_install.py

@@ -1,4 +1,5 @@
 import argparse
+import sys
 from pathlib import Path
 from subprocess import run
 
@@ -41,6 +42,9 @@ def main(args=None):
     """
     'protontricks-desktop-install' script entrypoint
     """
+    if args is None:
+        args = sys.argv[1:]
+
     parser = CustomArgumentParser(
         description=(
             "Install Protontricks application shortcuts for the local user\n"

src/protontricks/cli/launch.py

@@ -1,6 +1,7 @@
 import argparse
 import logging
 import shlex
+import sys
 from pathlib import Path
 
 from ..gui import (prompt_filesystem_access, select_steam_app_with_gui,
@@ -23,6 +24,9 @@ def main(args=None):
     """
     'protontricks-launch' script entrypoint
     """
+    if args is None:
+        args = sys.argv[1:]
+
     parser = CustomArgumentParser(
         description=(
             "Utility for launching Windows executables using Protontricks\n"

src/protontricks/cli/main.py

@@ -37,6 +37,9 @@ def main(args=None, steam_path=None, steam_root=None):
     """
     'protontricks' script entrypoint
     """
+    if args is None:
+        args = sys.argv[1:]
+
     parser = CustomArgumentParser(
         description=(
             "Wrapper for running Winetricks commands for "
@@ -154,11 +157,11 @@ def main(args=None, steam_path=None, steam_root=None):
         version=f"%(prog)s ({__version__})"
     )
 
-    args = parser.parse_args(args)
-
-    if len(sys.argv) < 2:
+    if len(args) == 0:
         # No arguments were provided, default to GUI
-        args.gui = True
+        args = ["--gui"]
+
+    args = parser.parse_args(args)
 
     # 'cli_error_handler' relies on this to know whether to use error dialog or
     # not

tests/cli/test_main.py

@@ -774,14 +774,10 @@ def test_run_gui_proton_incomplete(
 
     @pytest.mark.usefixtures("default_proton", "gui_provider")
     def test_run_no_args(
-            self, cli, steam_app_factory, command_mock, gui_provider,
-            monkeypatch):
+            self, cli, steam_app_factory, command_mock, gui_provider):
         """
         Run only the 'protontricks' command. This will default to GUI.
         """
-        # Monkeypatch 'sys.argv', as that seems to be the only way to determine
-        # whether no arguments were provided
-        monkeypatch.setattr(sys, "argv", ["protontricks"])
         steam_app_factory(name="Fake game", appid=10)
 
         result = cli([], expect_returncode=1)